This invention pertains to ultrafinishing metal surfaces and more particularly to the polishing of information handling disk metallic substrates.
As magnetic recording track densities and bit densities increase, it is necessary to enhance the precision of the accessing and transducer mechanism and the ability to discriminate between signal and noise with respect to the lesser magnitude signals being used. However, such technical achievements are unavailing if the cooperating storage media does not achieve similar higher levels of performance.
Such increased densities require that the media be formed of smaller magnetic particles disbursed in a thinner coating on a smoother substrate surface. The higher densities become even less tolerant of irregularities and discontinuities since smaller and smaller defects result in missing bits and unusable sectors or entire tracks.
The accepted finishing practice is to diamond turn the disk substrate which provides a relatively smooth planar surface which, although presenting a mirror finish, does include topography having a maximum peak to valley dimension that is 10 to 20 percent of the thickness of currently used coatings. This can cause signal irregularities which are tolerable, but when the coating thickness is reduced by half, localized thicknesses can be reduced by 20 to 40 percent by the substrate topography, which is unacceptable. To improve present media and enable the future use of thinner coatings, ultrafinishing of the diamond turned surface has become the practice. A common method is the use of a wax polishing pad and abrasive-laden slurry. This method improves the arithmetic average roughness of the surface, but does little to improve the maximum peak to valley differential. In addition, the abrasive particles are free to preferentially erode around the harder intermetallic sites at the substrate surfaces, often causing dislodging of such intermetallics and leaving pits.